Known moulds for the horizontal continuous casting of non-ferrous metals consist of a mould body, preferably manufactured from electro-graphite, in which a casting cavity is formed and which is enclosed by a casing made of metal, preferably copper. In this arrangement, the casing is designed with a cooling system. Electro-graphite is suitable for the manufacture of the mould body, particularly on account of its good sliding and self-lubricating properties, low wettability and good thermal conductivity.
For the horizontal continuous casting of ferrous metals, particularly of steel, a design, similar to that disclosed, for example, in U.S. Pat. No. 3,731,728, must be chosen, due to a possible reaction of the liquid metal with graphite. To protect the mould, a so-called inflow orifice, made of high quality material, is located on its inflow side, the open cross-section of this orifice being smaller, as appropriate, than the cross-section of the casting cavity. After the inflow orifice, in the direction of withdrawal of the continuous casting, a first mould part is provided, which effects the intensive cooling of the continuous casting. The length of the first mould part amounts to only a part of the length of the complete mould. The first mould part preferably consists of a copper mould tube, the cross-section of which corresponds to the cross-section of the continuous casting. There then follows a graphite mould of the type known for the casting of non-ferrous metals.
Subsequent to the initial formation of a solidified shell of continuous casting, this design takes advantage of the good sliding and self-lubricating properties of the graphite, the intrinsically very complicated introduction of releasing agents and/or lubricants thus being avoided.
As is evident from the periodical "Aluminium", Volume 5, 1975, from German Offenlegungsschrift No. 2,737,835 and from German Offenlegungsschrift No. 2,854,144, the siting of inflow orifices at the inlet position of moulds has also been disclosed with reference to the casting of non-ferrous metals.
The important difference, relative to the embodiments of moulds described above, resides in the fact that, in the case of moulds for casting steel, a short intensive cooling section is provided between the inflow orifice and the graphite mould, this section being made of a material with a high thermal conductivity. However, both these types of embodiment are disadvantageous, in that, following formation of the solidified shell of the continuous casting, the latter starts to pull away from the cooled mould wall, thus forming a shrinkage gap which restricts the heat transfer to such an extent that, due to the impairment of the mould cooling performance, the production performance of the mould is markedly reduced.
In order to bring about improved contact between the continuous casting and the inner wall of the mould and thus an improvement in the mould cooling performance, it has been proposed to shape the casting cavity of the mould with a conical taper in the direction of withdrawal of the continuous casting (concurrent cone). For example, the mould according to U.S. Pat. No. 3,731,728 is also designed to taper conically in this way.
In horizontal continuous casting, the continuous casting is predominantly withdrawn in a stepwise manner according either to the so-called go-stop procedure or, alternatively, according to the so-called pilger stepwise procedure, in which short reverse movements of the continuous casting occur after the withdrawal movement, or by a combination of these two procedures. At the metal inflow end, a mould part without tapering of the casting cavity is required, or, in the case of small cross-sections, a mould part is required which even has a casting cavity widening conically over several increments (reverse cone), in order to spare the relatively thin solidified shell of the continuous casting from subjection to excessive frictional forces. The beginning of the shrinkage gap, which causes a restriction in the cooling of the continuous casting, is also situated within the intensive cooling part, where the solidification of the metal commences. Due to the stepwise or also partly reverse movements, even a subsequent conical tapering of the casting cavity of the mould (concurrent cone) can produce no effective improvement in the cooling performance.
The object of the invention is accordingly to avoid the above-mentioned disadvantages, namely to ensure a good contact between the continuous casting and the wall of the casting cavity of the mould, for any mode of operation. That is to say, for example, it is desirable to produce this good contact also when reverse movements of the continuous casting occur.